My understanding is that as a rule of thumb, shooting steel should be at least 7 to 10 meters away from target. That is for outdoor ranges. Not sure about indoor.

I know at least 3 shooters who were hit by backsplatter
off a steel target (9mm and .45ACP) from 10-15 meters
off, all outdoors. I've been noggined by a .380ACP frag
from about 8: it raised a small bump right at the hairline.
I wasn't the shooter.

It's often said (TM) that a flat metal surface produces
smaller-particle backsplatter. It's pockmarked or else
dimpled surfaces that allow the freak occurrence of a
large piece coming right back at'cha.

Measures to limit the risk include targets that hang at a
slightly downward-facing angle (easy if you add weights
forward of the swingplate's lower edge to shift it's center
of gravity). Same goes for backstops: angle them facing
somewhat downward, so that any ricochets are directed
downward (preferably into water insead of sand, so that
the generation of lead-dust is minimzed)

If the support frame for a target swingplate is made out
of steel tubular, rotating the tubular so that the corners
(rather than the flats) face the shooter, helps.